Another Part of Civil Engineering

           The another part of civil engineering is Transportation engineering.This education is regarding  role of civil engineering in transportation.

           For Every mode of transportation civil engineering is basic essential education.
For example laying of roads and its development needs an civil engineer.
For Railways laying the tracks and construction of bridges on rivers also requires an civil engineer and also for construction of stations also required.
For Waterway transport such as construction of Port and Jetties also requires an  civil engineer.
For even Air way transport also an civil engineer because for construction of terminal ,laying of runway and its maintenance.

Retarders

Retarding admixtures:

                            

                             A retarded is an admixture that slows down the chemical admixtures and so that concrete remains plastic and workable for longer time than concrete without retarder.Retarder are used to overcome the accelerating effect of high temperature in hot weather concreting.

Action Of Retarders:

• Retarders delay the setting time of concrete cement.
• By forming a thin Coating on the cement particles and slowing down the resolution and reaction with water.By increasing the Intra molecular distances of reacting silicates and aluminates from water molecules by forming certain transcite compound in the system.
• Perhaps most commonly known as retarder sulphates.

          Ex:Sugar,starch,ferricor Ferrous Chloride,sodium Hexameta phosphate and sulphonic acid and their salts,carbonates and their salts.

Uses of Retarders

• Their Chief use of retarder in the hot weathering concreting which tends to reduce the setting time on account of high temperature and may allow completion of the concrete.
• Compassion finishing operations before initial set of the cement.
• In ready mix concrete where time element is involved in its transportation in mixing before it can be laid,compacted and finidhed.
• Use to obtain exposed aggregate look like concrete.Used in the growth of oil wells and concrete archs

Action of Accelerators and its Disadvantages.

Action of Accelerators:

                    The general action of accelerator are to cause more rapid chemical reaction and hence facility to increase more rapid hydration.For examples of accelerators are sulphated with an exception of calcium sulphates and alkali carbonates,Aluminates ,silicates ,Aluminium chloride,Calcium Chloride,Calcium phosphate,Formaldehyde and Potassium Hydroxide.

Disadvantages of Accelerators:

                     The Possess of CaCl2 results in flash set of Concrete and also increase Srinkage .How ever CaCl2 admixtures containing soluble chlorides and there not permitted to be used in Pre-stressed

Concrete.There are not used in concrete exposed to soils or water containing sulphates and this lowers the resistance of concrete subjected to sulphate attack.

Description of Air Entraining Admixtures

Air Entrainers:

               These are used to incorporate air in the form of minute bubbles in the concrete usually to increase the workability and resistance of freezing and Thawing.commonly used air entraining Admixtures are animal,vegetable oils,natural wood,Alkaline salts of sulphonated  organic compounds.

Factor Effecting the amount of air entraining:

               The manufacture of air entrained concrete is complicated by the fact that amount of air entrainment in a mix is effected by many factors.
The important factors are;

• Type and quantity of air entraining agent is used.
• Water by cement ratio is fixed.
• Types and grading of aggregates is done.
• Mixing Time
• Temperature
• Type of Cement
• Influence of Compaction
• Admixtures other than air entraining admixtures are used.

The Effect of Air Entrainers on the properties of the concrete:

            The air entraining will be affect directly on following properties of the concrete

• Increase in the resistance of freezing and thawing.
• Improvement in the workability.
• Reduction in the strength.

Incidentally air entrainment will also effect the properties of the concrete in the following ways

• Reduces the tendency of seggration
• Reduces the bleeding
• Decrease the permeability.
• Increase the Resistance.
• Permits the sand content which improves the plasticity and early finishing.
• Reduces the cement content,cost and heat of hydration.
• Reduces the unit weight.
• Permits the reduction in water content.
• Reduces the alkali-aggregate reaction.
• Reduces the Modulus of the Elasticity.

Classification of Admixtures

          The Classification of Admixtures are broadly classified in given below

1. Air entrainers 
2. Water Reduces
3. Retards
4. Accelerator
5. High Range water reduces plasticizers
6. Fine minerals
7. Specialty Admixtures

Introduction of Admixtures

                          These are the members of minerals used in cement.The cement motor and cement concrete these are minerals used,the used cement concrete that in order to improve their supply properties.

                        The admixtures are materials used other than three basic ingredients of cement concrete,these ingredients of cement concrete ,aggregates and water added to concrete mix before or during mix of concrete to improve certain properties in fresh or hardened state.

Function of Admixtures:

• To accelerate initial set of concrete i.e speedup the rate of development of strength at early age.
• To restart or delay.i.e delay initial state keep concrete workable for longer time for placement.
• To enhance the workability.
• To improve the penetration .
• To reduce the segregation in growth.
• To increase the strength of the concrete by reducing the water content and by densification of concrete.
• To increase the durability of the concrete .
• To reduce the capability flow of water to increase the permeability of the liquids.
• To inhabit the corrosion of reinforcement in the concrete.
• To reduce the heat of hydration.
• To increase the bond between old and new concrete surfaces.
• To enhance the bond of concrete and steel reinforcement.
• To produce non-skidding varing surface.
• To produce coloured concrete .
• To decrease the weight of the concrete. 

    

Setting Time of Water

                  Cement when mixed with water forms a paste which gradually becomes less plastic and finally hard mass is obtained.In this process setting stage is reached by the cement paste is sufficient visit to withstand a definite amount of  amount of pressure.A time to reach this stage is initial setting.
This Setting is divided in two types

1.  Initial Setting Time
2. Final Setting Time

Initial Setting Time:

                     The Time in which cement paste losses its plasticity is called Initial Setting Time.

Final Setting Time :

                      The time taken to reach take stage ,when the paste becomes hardness is known as Final Setting Time.

                      For O.B.C initial setting time should not be less than 30 minutes and final setting time should be 60 minutes.

                       Out of the 4 major compounds C3A reacts quickly with water to produce  jelly like compounds which start solidifies setting action is delay by adding gypsum at the grinding stage.Gypsum reacts with water   C3A to form tetra calcium Aluminiate hydrate and the setting time retarded to desired time.  

Fineness of Cement

             A fineness of Cement is measure size of the particles of the cement.

Penetration  Instrument

• It can be calculated from site distribution or from the One of the air permeability
• It is an important factor determining the rate gain of the strength and uniformity of the quantity.
• For given weight of the cement surface area is more for fineness cement than worse cement.
• The finer cement is higher than rate of the hydration as more surface available for chemical reaction resulting in the early development of the strength.The Effect of fineness on the compressive strength as shown in fig.

• If the cement is ground beyond certain limit ,it properties may be mixed adversely affected due to hydration by atmospheric moisture.
• Excessive fineness is also undesirable because cost of grindingness  of cement of higher degree of fineness is considerable and requires great amount of gypsum through rectangle.

• Fineness of Cement:

  Cement is measured in terms of % of weight and retained through 90mm seive.
  
  
  • Surface area of cement particular is sq.cm/gm.
  • IS 269-1967 specifies that maximum residue after seeing through 90umm should be limit 105 of OPC.
  • IS  269-1967 specifies air permeability and lays down that specifies surface in sq.cm/gm of cement and calculated by this method shouldn't less than 2530 sq.cm/gm.